Preliminary studies on eutrophication and red tide problems in Bohai Bay

A study was carried out in 1978–1981 on the relationship between eutrophication and the occurrence of red tides in Bohai Bay.An assessment method using a single parameter as well as the multiparameter Trophic State Index was adopted. DIN, DIP, COD loadings and concentrations and phytoplankton community (species composition, diversity index, standing crop, chlorophyll a and primary productivity) were used as parameters. The western part of the bay and two sewage outfall sites showed the highest values of chlorophyll a, nitrate, phosphate, standing crop, primary productivity and the greatest population instability. Therefore, Bohai Bay, can be regarded as mesotrophic, but its estuary eutrophic. Anthropogenic factors are mainly responsible for its eutrophication. A relationship between environmental factors and red tide species was found. Noctiluca miliaris, Prorocentrum minimum and Skeletonema costatum have their bloom periods from July to September and are the most significant species.